As a relative newbie that entered Wikipedia during the full flower of disambiguation pages, I'd like to give my response to the discussion so far.
I think it's clear that some ambiguous pages, most obviously [[Paris]] but also for that matter [[Virus]], should be primarily about the most common sense of the term, while other pages such as [[Venus]] should only disambiguate. However, the difference between these examples is not vital and can safely be decided on a case by case basis.
What's important to me is that Bryan Derksen is right, and we should make sure that he continues to be right: If a writer makes a spontaneous link to an ambiguous name, then readers can get to the right page after one more link. Is it ideal that the link read "[[Mercury (planet)|Mercury]]" rather than just "[[Mercury]]"? Yes. Is it necessary? No. I can easily imagine a writer in the heat of a computer article typing "[[worm]]" without thinking if that makes global sense, but if they do, then this causes only minimal damage. The encyclopaedia is still readable, even easily so, as long as the article [[Worm]] begins something like
"''This article is about worms, the animals. There is also a Wikipedia article about [[computer worm]]s.'' " "---- " "A '''worm''' is any of numerous relatively small elongated soft-bodied etc.
(Currently, the computer bit is at the bottom, which I too don't like. But I think that it's important to keep the top stuff *short* -- get people to the right page, and then start the article.)
As a reader, disambiguation pages have worked for me. As a writer, I try to link directly but I know that I make mistakes; I hope that disambiguation pages are there to catch them.
-- Toby Bartels toby@math.ucr.edu
PS:
You know what would make writing unambiguous links easier? I'd like to say "[[Mercury (planet)|Mercury]]" without repeating "Mercury". Would it work to have a feature such that, say, "[[Mercury]](planet)" (with no space) produces that effect?